1. Technical Field
The present technology relates to an image display system, an image composing and re-encoding apparatus, an image display apparatus, a method of displaying an image, and a computer-readable storage medium having stored therein an image composing and re-encoding program that compose a plurality of images captured by a plurality of cameras and display a composed image.
2. Related Art
Generally, image display systems are known which compose a plurality of images captured by a plurality of cameras and display a composed image. According to such an image display system, for example, by generating a composed image in which images captured by four cameras are aligned vertically and horizontally, the four images captured by the four cameras can be displayed altogether as one image.
In JP 2009-21983 A, as such an image display system, a monitoring image recording apparatus for the purpose of reducing a difference in the response time by improving responsiveness at the time of reproducing multiple screens is disclosed. FIG. 10 is a block diagram that illustrates the configuration of the monitoring image recording apparatus. The monitoring image recording apparatus 10 includes a network interface 11, MPEG decoders 12a to 12d, memories 13a to 13d, H.264 encoders 14a to 14d, an image recognizing unit 15, an encoding control unit 16, a recording control unit 17, a recording device 18, H.264 decoders 19a to 19d, and a composition unit 20.
Encoded streams of images of a plurality of channels that are captured and encoded by a plurality of cameras 1a to 1d are transmitted to the monitoring image recording apparatus 10 through a network 2. The network interface 11 of the monitoring image recording apparatus 10 distributes the encoded streams to the MPEG decoders 12a to 12d corresponding to respective channels (cameras). The MPEG decoders 12a to 12d decode the encoded streams of the channels, temporarily stores decoded images in the memories 13a to 13d, and transmit the decoded images to the image recognizing unit 15 that determines the occurrence of an event by performing image recognition of decoded images. The image recognizing unit 15 performs motion detection and face detection by taking a background difference, determines whether an event occurs in an image, and outputs event information relating to the occurrence of the event.
In this monitoring image recording apparatus 10, a group of pictures (GOP) included in the encoded stream is used as a constituent unit of a moving image. A start frame and an end frame of the GOP are defined based on information of a GOP start position and a GOP size. The encoding control unit 16 receives the occurrence of an even that has been determined by the image recognizing unit 15, generates encoding information that includes the GOP start position, the GOP size, and a re-coded rate based on event information, and outputs the generated encoding information.
The H.264 encoders 14a to 14d encode the decoded images of respective channels stored in the memories 13a to 13d based on the encoding information of the encoding control unit 16 and outputs re-encoded streams. Here, in the encoding information that is generated and output by the encoding control unit 16, the GOP start positions and the GOP sizes are determined such that the H.264 encoders 14a to 14d perform re-encoding in a state in which the GOP sizes and the start positions of all the channels are uniformized in accordance with the occurrence of an event.
The recording control unit 17 generates a management table including the event information and the encoding information as image management information used for managing the re-encoded streams and the event information transmitted from the image recognizing unit 15 altogether and records the re-encoded streams in the recording device 18 in association with the image management information based on the management table.
In a case where an image recorded in the recording device 18 is reproduced, and more particularly, in a case where a plurality of images are reproduced, the recording control unit 17 reads the re-encoded streams of respective channels corresponding to the event from the recording device 18 by referring to the image management information of the management table. Then, the re-encoded streams of the respective channels are decoded by the H.264 decoders 19a to 19d, a multi-screen composing process is performed by the composition unit 20, and resultant images are output. From this, recorded images are displayed on multi-screens in a monitoring monitor 3. In other words, images of four moving images of channels a, b, c, and d can be displayed as multiple screens on one display screen.
Particularly, in the monitoring image recording apparatus 10, start frames and end frames of the GOPs of the moving images of a plurality of channels are determined by the encoding control unit 16 based on the event information relating to the occurrence of an event and apparatus setting information, and the start points of the GOPs of the re-encoding streams are uniformized for a plurality of channels by the H.264 encoders 14a to 14d, and the re-encoding streams are re-encoded.
FIG. 11A is a diagram that illustrates the configuration of encoding streams of respective channels in a case where the sizes and the start positions of GOPs are not uniformized, and FIG. 11B is a diagram that illustrates the configuration of encoding streams of respective channels in a case where the sizes and the start positions of GOPs are uniformized. As illustrated in FIG. 11B, in a case where an event occurs, the sizes and the start positions of GOPs can be uniformized in accordance therewith, and accordingly, a difference in the response time at the time of multi-screen reproduction can be reduced.
However, in a case where the conventional image display system described above is applied to an image display system that composes a plurality of pieces of image data received from a plurality of cameras through a wireless network, re-encodes a composed image, transmits the re-encoded composed image to an image display apparatus, and displays the composed image decoded by the image display apparatus in real time, there is a case where composition and re-encoding as described above may not be realized due to transmission fluctuations in wireless communication.